Heart failure is a major cause of death in the developed and developing world; it is estimated that there are currently 901,500 sufferers in the United Kingdom with 65,000 new cases added annually. The British Heart Foundation estimates the annual cost of heart failure is £625 million in the UK alone. In the United States, the corresponding statistics are 5,000,000 sufferers with 550,000 new cases annually and an annual cost to the US economy of $296,000 million. The World Health Organisation estimates that Cardiovascular Disease, around 7% of which is heart failure, contributed to ⅓ of all deaths worldwide and will be the major cause of death by 2010.
The prognosis for heart failure sufferers is poor, with just less than 40% dying within the first year. Furthermore, 5% of all deaths in the UK, approximately 24,000 per annum, are attributable to heart failure. Around 40% of these patients suffer from impaired left ventricular systolic function and could benefit from mechanical support e.g. with a Left Ventricular Assist Device (LVAD). The best therapy for many of these patients would be heart transplantation; however the demand for donor hearts in the USA alone is around 100,000 per annum and far exceeds the 2,200 donor hearts available per annum. The other main therapies commonly available are medical, such as inotropes, ACE inhibitors, Beta blockers, diuretics and nitrates, or are mechanical support therapies, such as the use of a Total Artificial Hearts (TAHs) or Ventricular Assist Devices.
There is a continuum of treatment modalities for patients suffering chronic heart failure. As the disease progresses patients will receive increasingly aggressive medical therapies, but most patients become refractory to medical therapies at some point and their health will decline. Patients eligible for cardiac transplantation would typically receive medical therapies whilst awaiting transplantation; if their condition deteriorated then mechanical “bridge to transplantation”, may be adopted in the form of a mechanical support device such as an Intra-Aortic Balloon Pump (IABP), Extra-Aortic Balloon Pump (EABP), or other LVAD. Patients who are supported in bridge to transplantation whilst awaiting transplantation are in a better state of health at the time of transplantation, are more likely to survive transplant surgery and have a better long-term prognosis. Patients ineligible for transplantation typically follow a medical therapy-only path, though with the most aggressive health-care providers may receive mechanical support, e.g. a LVAD or a TAH in “destination therapy”.
Several mechanical devices are currently available or are in development which support cardiac function in heart failure. Rotary Blood Pumps (RBPs) take blood typically from the ventricle of the native heart, energise it through the action of a rotating impeller, and deliver the blood to the ascending aorta. These devices allow the patient to ambulate, but do not produce pulsatile blood flow as does the native heart. In contrast, RBPs typically act at a constant rotational speed, can be difficult to control, and are expensive in their implanted form. IABPs, such as those described in U.S. Pat. No. 6,210,318 and EP0192574, are well established technology and comprise small balloons which are inserted into the aorta and which are inflated and deflated, typically in anti-phase with the native heart, through the action of pneumatic fluid acting behind a flexible polymeric membrane. IABPs cannot be deployed for long periods of time since their thin silicone membranes are prone to rupture and their cannulae can cause thromboembolism. EABPs, such as those described in EP1318848, EP1560614, and U.S. Pat. No. 4,733,652, address some of the problems with IABPs through being attached to the external surface of the aorta rather than being implanted within the aorta. Disadvantages of EABPs can include atheromous emboli through interaction with the aortic wall, and migration and interference with neighbouring structures, e.g. erosion of the pulmonary artery or lungs. Other technologies which similarly augment blood flow using balloon pumps include: a balloon pump for insertion into the descending aorta described in U.S. Pat. No. 6,030,355, but this device has a rigid outer body which precludes its implantation at the optimal position in the lower ascending aorta where pumping effect is optimised; and the conduit mounted balloon pumps described in U.S. Pat. Nos. 4,195,623 and 4,015,590 which similarly are non-optimally positioned.
The present invention seeks to provide an alternative pump which provides various advantages over those of the prior art when used in cardiac support.